Discharge check, valves

Suction and Discharge Shutdown Valves and Discharge Check Valves... 

A pump case in hot service should be heated evenly prior to starting or switching the pump. This is usually done by the warm-up valve on the pump discharge. This valve bypasses the discharge check valve, thus permitting the hot liquid being pumped by the primary pump to back into and preheat the spare pump that is being put online. 

One of the problems with the use of ordinary barrier seals is that they will be ruined if a pump spins backward, even briefly. This will happen when a pump is shut down after turning on the spare pump, if the discharge check valve leaks. 

For larger pumps with the suction on top of the pump case, a spill-back warm-up line connected to the case is needed to evenly warm up the pump. For all hot pumps, a spill-back bypass is needed aroimd the pump s discharge check valve for warm-up when switching pumps. 

Open the spillback around the discharge check valve to warm the pump case. For pumps with the suction on top of the pump s case, open the connection allowing the hot spill-back flow to recirculate to the bottom of the pump. The suction valve needs to be partly open. Wait until the pump case is uniformly warm. Starting a pump that is cold or unevenly... 

Fig. 2. Single-acting metering system. A, B—material tanks C, D—discharge check valves E, F—charge check valves G—drive cylinder H—mixer PA resin cylinder PB—hardener cylinder V—hardener bypass valve.

The pump is equipped with all-welded, double-ball, gravity-operated suction and discharge check valves. The 1-in. balls operate in close-fitting cages (0.010-in. diametral clearance) which maintain the alignment of the ball and scat and restrict the ball lift to 0.125 in. 

Check the discharge block valve opening first. It may be partially closed and thus the problem. 

Install check valve in distillate discharge line... 

Internal Re-circulation Operation / Design / Maintenance Internal Re-circulation results from something in the discharge side of the pump strangled valve, clogged filter, over-pressurized header, check-valve installed backwards. 

A pipe size incrcascr can be used in the discharge piping. This will reduce the fluid velocity and friction losses. An isolation valve with a low loss characteristic such as a gate valve should he placed after the increaser and check valve. 

Check valves must be used on each pump discharge to prevent backflow through the idle pump. On those systems where a flooded suction is not furnished, an orificed bypass around the appropriate check valve should be furnished to keep the suction line of the non-flooded suction... 

In order to avoid the need to measure velocity head, the loop piping must be sized to have a velocity pressure less than 5% of the static pressure. Flow conditions at the required overload capacity should be checked for critical pressure drop to ensure that valves are adequately sized. For ease of control, the loop gas cooler is usually placed downstream of the discharge throttle valve. Care should be taken to check that choke flow will not occur in the cooler tubes. Another cause of concern is cooler heat capacity and/or cooling water approach temperature. A check of these items, especially with regard to expected ambient condi-... 

Suction ond Discharge Shut-down Valves, Discharge Check... 

A more serious incident occurred at a plant in which ethylene oxide and aqueous ammonia were reacted to produce ethanolamine. Some ammonia got back into the ethylene oxide storage tank, past several check valves in series and a positive pump. It got past the pump through the relief valve, which discharged into the pump suction line. The ammonia reacted with 30 m of ethylene oxide in the storage tank. There w as a violent rupture of the tank, followed by an explosion of the vapor cloud, which caused damage and destruction over a wide area [4],... 

Cascading effects Check valve Clogged (of filter) Consensus standard Conservation vent Dike, berm Discharge valve Division (in electrical area classification) Downspout Expansion joint Explosion proof Faucet... 

Terminate discharge pipe below liquid level or add a couple of elbows or a swing check valve to provide enough back pressure for elector to "seal". 

For conventional valves, pressure drop or variations in back pressure should not exceed 10% of set pressure. Because most process safety valves are sized for critical pressure conditions, the piping must accommodate the capacity required for valve relief and not have the pressure at the end of vent or manifold exceed the critical pressure. Designing for pressure 30% to 40% of critical w ith balanced valves, yields smaller pipes yet allows proper functioning of the valve. The discharge line size must not be smaller than the valve discharge. Check the manufacturer for valve performance under particular conditions, especially with balanced valves w hich can handle up to 70% to 80% of set pressure as back pressure. 

During the discharge stroke, the inlet check valve is closed. Condensate draining from the steam space then fills the inlet piping. Unless the piping is sufficiently large or contains a receiver section (reservoir), condensate could back up into the steam space being drained. 

Ensuring the pressure in the air blower discharge piping system, particularly across the check valve and air preheater, is not excessive... 

Toluene is to be pumped between two vessels using a centrifugal pump with a flowrate of 30t h 1. The pipe diameter is 80 mm (internal diameter 77.93 mm). The pipeline is 35 m long, with 4 isolation valves (plug cock), a check valve and 5 bends. The discharge tank is 3 m in elevation above the feed tank. The density of toluene is 778 kgrn 3 and viscosity of 0.251 x 10 3 N-s-rn 2. 

On June 22, 1997, an explosion and fire destroyed an olefin plant at the Shell Deer Park, Texas chemical complex. Thirty workers received minor injuries and extensive damage resulted to both the plant and adjacent community. The incident was caused by the sudden failure of a pneumatic check valve in a 300-psig gas compressor discharge line that led to a large release of propylene vapor. A few minutes after the release, the gas ignited causing a vapor cloud explosion and flash fire. 

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